A gas electrode is an electrochemical electrode for conducting oxidation or reduction of a gaseous component. It has been developed especially for use as a fuel cell. Electrolytes to be used in a gas electrode include phosphoric acid, a molten salt, and a solid electrolyte. In recent years, fuel cells using a solid polymer electrolyte (ion-exchange membrane) has been attracting attention for their low working temperatures. In the field of industrial electrolysis, too, a solid polymer electrolyte is known to be useful in electrolysis of water or electrolytic production of ozone. A gas electrode can be used as such as an electrolytic electrode for gas evolution, or it can also serve as a hydrogen pump or an oxygen pump. It can also serve as an oxygen gas electrode as a negative pole for electrolytically producing ozone without being accompanied by hydrogen evolution.
A gas electrode is generally comprised of a conductive porous material, and it is important to optimize the state of the interfaces of the three phases consisting of a gaseous phase, a liquid phase, and a solid phase. A gas electrode is generally produced by mixing conductive carbon fine powder and a hydrophobic fluorine resin powder or a suspension thereof, forming the mixture into a sheet, and sintering the sheet. An electrode catalyst may previously be added to carbon powder in a wet process, as disclosed in JP-A-57-152479 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), or a catalyst solution may be applied to a sheet gas electrode and then sintered (see JP-A-62-156268). The former process has conventionally been used for the advantage that a homogeneous and fine platinum group metal catalyst can be supported. However, the process has a considerably low productivity when carried out on an industrial scale because the bath is difficult to control, and the yield is low. The latter process is economically advantageous because of satisfactory yield. However, it is difficult to control the catalyst particle size. Additionally, the process involves a practical problem since a dangerous material, such as hydrogen gas, is used in calcination.